Cyber-Physical (CP) systems must address engineering domains such as automotive, petrochemical, aerospace, manufacturing, civil infrastructure, and medical device systems, with an eye to how the fault tolerance, security, decentralized control, and social aspects of these systems influence their design. Bulk power transmission systems are one such CP system and form a rich environment for the study of several inherent problems. First, these systems form one of the largest and most complexly inter-connected networks ever built, and their scale makes controlling them extremely difficult. Recent federal mandates for deregulation further increase the difficulty of control. Heavier power transfers resulting from independent ownership and potentially widespread use of distributed energy generation will make power systems increasingly vulnerable to cascading failures in which a small series of events can lead to a major blackout. The envisioned Advanced Power Grid must include support for decentralized energy generation and transmission controllers, whose local actions can be coordinated for integrated and efficient control of the power grid as a whole.